1. Field of the Invention
This invention relates to a time switch for controlling a load at a predetermined time.
2. Description of the Related Art
FIG. 18 illustrates an example of this kind of time switch as related art. This time switch includes a boxed-shaped main casing 11 having a front opened end, a printed circuit board 32xe2x80x2 placed in the main casing 11, and an inner cover plate 12 covering the front opened end of the main casing 11.
The printed circuit board 32xe2x80x2 is equipped with a clock function block 21 having a liquid crystal display and a plurality of push buttons, a terminal block 22 for connecting loads, and a load controlling relay 23. The circuit board 32xe2x80x2 is fitted in and fixed to the main casing 11 by tightening screws 13. The main casing 11 is coved by an outer cover (not shown). The inner cover plate 12 is disposed at the front opened end so as to cover the whole area of the printed circuit board 32xe2x80x2 and fixed to the main casing 11 by tightening screws 14. In this state, the clock function block 21 is exposed through the opening 12a formed in the inner cover plate 12.
However, according to the aforementioned structure, when loads are connected the terminal block 22, since the inner cover plate 12 covers not only the circuit board 32xe2x80x2 but also the terminal block 22, the inner cover plate 12 should be detached from the main casing 11. As a result, the whole area of the circuit board 32xe2x80x2 (i.e. the parts provided on the circuit boards 32xe2x80x2 ) will be exposed. This allows a wire of the load and/or a tool such as a screwdriver to contact the parts, resulting in unintentional damages to the parts. Furthermore, since the circuit board 32xe2x80x2 is exposed during the connecting operation of the load, foreign substances may adhere to the parts circuit boards 32xe2x80x2 and/or the load. This may also cause a breakage problem thereof. In addition, the clock function block is complicated in structure, resulting in an increased manufacturing cost.
U.S. Pat. No. 5,329,082 discloses a time switch equipped with a mechanical clock function block mounted on a plastic plate and a circuit board having a terminal block. The circuit board is also connected to the plastic plate so that the terminal block is exposed. According to this construction, a connecting operation of the load to the terminal block may be performed without causing any problems or damages to the clock function block, and an adherence by foreign substances can be avoided. Thus, unexpected damages of the clock function block or accidents may be avoided. However, since the terminal block is fixed to the plastic plate together with the clock function block, in a case where different types of time switches are manufactured, it is required to manufacture different types of terminal blocks designed for the respective type of time switch. Thus, the terminal block cannot be used for different types of time switch, resulting in an increased manufacturing cost.
Furthermore, in this structure, in a case where a quality testing is performed to confirm the functions at the stage of designing the product, it is required to evaluate not only the clock function block but also the terminal block. Thus, a larger number of points should be checked as compared to only checking the clock function block, which causes an increased labor for the evaluation.
An object of the present invention is to provide a time switch which is simple in structure and low in manufacturing cost.
Another object of the present invention is to provide a time switch in which an connecting operation of a load to a terminal block can be performed without causing any damages or problems.
Still another object of the present invention is to provide a time switch which can easily perform an evaluation test.
Yet another object of the present invention is to provide a time switch having a common part which can be used for different types of time switches.
According to a first aspect of the present invention, a time switch includes a circuit board equipped with a time switch circuit and a display for displaying a time-schedule set by a user and a current time, an operation unit having a plurality of push buttons for setting the time-schedule and the current time, and a casing in which the circuit board and the operation unit are accommodated, the casing having a plurality of openings for fitting the plurality of push buttons. The operation unit includes a resilient sheet member integrally equipped with the plurality of push buttons and a plurality of conductive contact members each disposed on a portion corresponding to each of the plurality of push buttons. The circuit board has pairs of contact portions. Each pair of the contact portions is to be electrically connected via the conductive contact member while the push button is being depressed. The operation unit is supported by the casing and the circuit board in a state that a peripheral portion of the sheet member is clamped by and between an inner surface of the casing and the circuit board with the plurality of push buttons fitted in the plurality of openings.
With this time switch, since the operation unit is supported by the casing and the circuit board, the time switch can be simple in structure, resulting in an easy assembly and a reduced manufacturing cost.
According to a second aspect of the present invention, a time switch includes a circuit board equipped with a time switch circuit and a display for displaying a time-schedule set by a user and a current time, an operation unit having a plurality of buttons for setting the time-schedule and the current time, a casing in which the circuit board and the operation unit are accommodated, the casing having a plurality of openings for fitting switches and pilot lamps provided on the circuit board, and a display sheet attached on a surface of the casing, the display sheet having a plurality of openings for exposing the switches and pilot lamps. The number of the openings formed in the casing corresponds to the maximum number of the switches and pilots lamps to be provided on the circuit board. Furthermore, the number of the opening formed in the display sheet corresponds to the number of the switches and pilots lamps actually provided on the circuit board, whereby some of the opening formed in the casing not in use are covered by the display sheet.
With this time switch, even in a case where the operation of the circuit board and/or the number of parts provided on the circuit board are changed, it is only required to change a display sheet to be attached on the casing. In other words, it is not required to change the casing. As a result, the storage space can be decreased, and various types of time switches can easily be provided.
Other objects and advantages of the present invention will become apparent from the description of the preferred embodiments, which may be modified in any manner without departing from the scope and spirit of the present invention.